“Soft-feel effect” in the context of the present invention refers to a particular touch sensation (haptic quality) of the coated surface. This haptic quality can be expressed by terms such as velvety, soft, rubber-like or warm, whereas, say, the surface of the coated car body or else a plastic sheet (e.g. ABS, Makrolon) or plexiglass, uncoated or coated with a conventional clearcoat or topcoat material, feels smooth and cold. EP-A 0 529 094 describes, for example, a solvent-based surface coating with soft-feel effect, the haptic quality there being achieved through the combination of a urethane resin with elastic particles or with a porous inorganic material.
Modern aqueous coating compositions are capable of substituting for binders in organic solution in many applications. However, for certain applications with specific profiles of requirements, such as the coating of substrates, and more particularly plastics substrates, with soft-feel effect coating materials, for example, there has to date been a lack of aqueous binders which meet all of the requirements imposed, particularly those concerning the resistance properties of the films. Thus, for example, EP-A 0 358 979 describes aqueous two-component reactive polyurethane systems based on secondary dispersions of vinyl polymer and on polyisocyanate crosslinkers, which already have a good level of properties, particularly as far as resistance to solvents and other chemicals is concerned. Nevertheless the target haptic quality of soft feel cannot be achieved with these coating compositions.
EP-A 0 669 352 describes special aqueous polyester-polyurethane dispersions which, in combination with crosslinker resins and, where appropriate, with linear, hydroxyl-free polyurethane dispersions, can be cured to give coatings having a good soft-feel effect, good mechanical properties, and a generally satisfactory solvent resistance. For certain applications, however, the resistance, particularly the resistance to suntan lotion, are still in need of improvement.
EP-A 0 926 172 describes aqueous two-component (2K) polyurethane coating materials in which the resistance to suntan lotion (which penetrates the film, causing delamination and/or other damage) can be improved by using special ester-modified polyisocyanates. The binders used in that case are mixtures of carboxylate- and/or sulfonate-hydrophilicized polyester polyol dispersions with physically drying, carboxylate- and/or sulfonate-hydrophilicized polyurethane dispersions.
An object of the present invention was to provide a new polyurethane resin which can be processed to aqueous coating compositions which have good resistance, particularly to damage caused by exposure to suntan lotion, and at the same time, in the form of the film, had a pronounced soft-feel effect. The polyurethane resins ought also to be readily processable with the commercially available hydrophilicized or unhydrophilicized polyisocyanates to form coating systems.